Tonebender MK II clone problem

[Leepyringa]

I built my tonebender with parts from smallbearelec.com ... everything was working fine!

But once when I engaged that pedal , all that i got is white noise and a slight fart ...I removed my pcb and all jacks and pot from enclosure , checked all connections but still don't know what's wrong ... when I put it all back into enclosure it was working fine! Then it repeated the next day

I have no idea what might be a problem ! One of my friends said that this sounds like a static charge ...

Please help me! 

[LucifersTrip]

first thing you do is take voltages when working and compare to when it's not.

...if you leave it outside the box, will it continue to work? if so, look for shorts with the enclosure when boxed.

if it dies either way, I'd start looking for bad connections...something intermittent. re-flow solder joints

[Leepyringa]

Thanks! that's a good idea but i can't get it to work anymore ... it's off for two days now..

I left it outside the enclosure but problem still exist . all wires were resoldered but it's still here

Though , I get some sound when it's attack pot is on half  ... something fuzzy-like but very quiet and farty...And quiet clean sound on it's attack full way up

Must be something with my pcb ,though i checked all the connections and it seemed to be ok

[Leepyringa]

btw here's the schematic ... reds are resistors i changed to smallbearelec.com specs

voltages on :
Q1:
Vcb = 0
Vce = 0
Veb = 0

Q2:
Vcb = 0.25 v
Vce = 0.34 v
Veb = 0.08 v

Q3:
Vcb = 0.12
Vce = 0
Veb = 0.13 v

When it's worked voltages were about
Q1 Vc  = 8.11V
Q2 Vc = 1.10V
Q3 Vc  = 4.5V

So I'll look further and will try to trace voltages loss

[Leepyringa]

Yep , everything's working fine now ! thanks for the advice ... I resoldered everything and maybe it wasn't working because i spilled there rosin more than enough

[LucifersTrip]

sounds cool...remember to record voltages when it sounds best so you always have a reference to get back to

I will make one note that you might not want to hear now...Q3Vc should be around 7 - 8v+.  Unfortunately, many have been burned by the incorrect info at Fuzz Central. I emailed them, but no response....

http://stompboxes.co.uk/forum/viewtopic.php?f=10&t=7185&p=110299#p110299

[Leepyringa]

I have now Q1 Vc = 8.5
                 Q2 Vc = 1.2
                 Q3 Vc = 2

It sounds killer! maybe too killer ... it has huge sustain but i think too much top ... any ideas to make signal less toppy ?

[Leepyringa]

btw , when Q3 Vc set to 4.5 it sounds noisy and wrong ...

[Leepyringa]

Oh sorry I messed up!) mine Q3 is 8 volts , everything's right ! thanks by the way!

[LucifersTrip]

what do you mean by toppy?

At 4.5v it shouldn't really be noisy, but thinner and more saturated ...and lower volume

Everybody has different experiences with these and likes em biased differently. I usually like Q3 in the 7 - 7.5v range, where I still have some of the saturated fuzz that you'd get at 4.5v but not the full boom you'd get at 8 - 8.5v.   When you get up there (>8v), it's typical to get some gating, which is one of the things people like about some MKII's.

Also, it is recommended by many to bias Q3 with the resistor off of Q2C.

[Leepyringa]

I was sitting all day playing with tone bender ) and ended with Q2 C resistor ~15K and Q3 C is about 15K also ... sounds the best with their hfe! I forgot to measure voltage and i'm too lazy to do it now

[bluesdevil]

If it sounds too bright. try tacking on a .001uf cap from output to ground.... worked great with the smallbear tonebender set I got years ago. You can do this on the volume pot's lugs.

[LucifersTrip]

The .01uf to ground at the input should take care of any over-brigtness if that's a problem. That .01uF is not in all units and is listed as "optional" in other schematics
http://forum.musikding.de/cpg/albums/userpics/16602/MKIIOC75schem.png

[Leepyringa]

Thanks guys! I have a set from small bear too but it looks that mine Q3 is burned now ( and this may cause harshness and all ...

I'm very sad now cause yesterday i broke my ac adapter and ehx holy grail and now tone bender's gone wrong ... will try to find any replacements for my oc75

[Leepyringa]

I think I'll look for ac125's ... btw i'm bad at electronics , how did i manage to burn my oc75 ? I was playing with Q2 collector resistor and Q3 collector resistor at range from 0 to 20K ohm ... it would be really helpful to know

[Leepyringa]

So if anyone's interested i changed burned oc75 on Q3 to мп41а . It's a russian tranny with hfe = 90 and all together it sounds incredibly sweet! I set voltage at Q3 Vc at about 8.5 v

Also cap at the end solved my problem of overbrightness so thanks again , bluesdevil !)